Squats,lunges,deadlift,leg curls,plyometrics can. I added 6 inches to my vertical by doing sprint training with a resistance band. Do a bit of calf work too but the majority of your vertical comes from your glutes hams and quads.

You shouldn't buy store weight gainers, make your own. There are a few recipes that have been posted in this subreddit before. A lot of store bought weight gainers are just loaded with sugar or other things. If you are eating these shakes and you are eating more than your TDEE than yes you will gain weight.